Ultrasound elastography is an important method for assisting cancer detection, in particular mammary cancer detection, in B mode ultrasound images, which is widely used in clinic. Ultrasound elastography mainly acquires ultrasound echoes from target tissues by ultrasound imaging, detects information about tissue elasticity using particular algorithms, and visually displays the information in the form of images, so as to assist doctors to make a diagnosis or therapy.
Conventional ultrasound elastography acquires two frames of ultrasound echo signals in succession by slightly compressing the tissue using a probe or with the assistance of a patient's breathing or vascular pulsation process, etc., and then determines the displacement (which is the change of the spatial location of the target tissue at two different times) between the two signal frames by particular displacement detection methods. Then, the axial strain of the tissue can be calculated from the axial gradient of the displacement. This axial strain may represent the elasticity of the tissue. Under the same external compressive force, the larger the strain, the softer the tissue; the smaller the strain, the harder the tissue. The strain of a target tissue may be displayed in the form of images, which can visually show the difference of hardness or elasticity between different tissues. These images are called strain images. This method is also referred to as strain imaging.
In the process described above, the contrast-to-noise ratio (CNR) of the resulting strain images, whether it may be achieved in real time, and whether the frame rate can meet clinical needs, etc. may be affected by whether the displacement can be correctly detected and whether the calculation can be done rapidly. Conventional methods for detecting displacement are usually categorized into three categories: the time domain detection methods based on cross-correlation, the methods based on phase shift, and the methods based on tissue Doppler imaging (TDI). The methods based on cross-correlation may obtain images with good quality, but often require a large amount of calculation and particular echo data sampling rate. The methods based on phase shift can be fast, but there may be phase aliasing, so they can be more suitable for the situations with small displacements and may generally ignore the lateral displacement, and can result relatively poor image quality. The methods based on TDI can be easily implemented, but may depend on the signal-to-noise ratio (SNR) of the Doppler signals and on the processing methods, and may still have phase aliasing and also ignore the lateral displacement and have relatively poor image quality.